So I plan to lower the car with H&R spacers unless Eibach starts selling their springs by the time my car arrives. I just wanted to know if anyone's lowered their car and if they've installed spacers, and if so what size?

Right now, KW only has the Clubsport or V3 available, I asked KW for a sleeve kit which does not mess around the electronic dampers and KW has no intention of making such kit in the near future. The V3 will require to delete (deactivate) the factory electronic damper and that's why I may just do the springs. Eibach is my preferred choice.

I had Eibach's on both my M5's, and H&R's on my X6. Eibach is also my preferred choice but I'm very impulsive and impatient so I will most likely go with the H&R's. If I don't like them Ill swap them out.

You can also get the ACS springs which are available today (590$) , I recently had the chance to drive in a F10 M5 with ACS springs and my opinion is they actually have better ride comfort than the H&R springs which tend to make the car bouncy (had them in the past and they made me go for a full coilover kit even faster) . The ACS springs however will lower the car slightly less than the H&R springs.